Projection televisions typically use cathode ray tubes (CRTs) which display an image on a glass faceplate. That image is projected through a coupler and lens assembly onto a screen of the television. The coupler is typically formed as a separate component of die cast aluminum and serves to couple the CRT to the lens assembly and also to secure the coupler/lens assembly as a unit to appropriate mounting structure within the television cabinet. In rear projection type televisions, three such CRT units are used to project the same image in the three primary colors onto a mirror with the image being reflected and magnified onto the viewing screen.
A “C” lens of the lens assembly is mounted to a side of the coupler opposite to the CRT. As each of the three CRT's in a projection television most often operate at maximum power so as to maximize light intensity at the CRT faceplate, and as each CRT is located within the confines of a projection television cabinet, considerable heat is generated in the vicinity of each CRT. Such heat can have undesirable effects on the lens assembly, such as changes in the focus of the lens assembly. This can lead to significant image distortions on the television screen. In addition, such heat can lead to extreme temperature gradients on faceplate of CRT possibly causing a shortened CRT life. Therefore, a liquid coolant, such as an ethylene glycol/glycerin coolant, is contained between the “C” lens and the CRT faceplate in a sealed space defined within the die cast aluminum coupler to provide a more uniform temperature on the CRT faceplate. An additional benefit of filling the volume between CRT faceplate and “C” lens with this liquid is to improve the contrast of the lens system. The coupler may be coated with a nonreflective dark finish, such as a black paint or other coating to improve contrast by reducing light reflections and to prevent corrosion of the aluminum casting.
Various problems or drawbacks with current systems utilizing separate die cast aluminum couplers include the increased number of parts and increased assembly. In addition, the use of increased numbers of components in the overall assembly necessarily leads to an increase in tolerance stack up and, therefore, less overall dimensional accuracy in the assembled product. In the case of a lens and CRT assembly for use in a projection television this may lead to additional distortion in the image projected onto the television screen. Another disadvantage in using a CRT coupler with nonreflective surface finish such as black paint or other coating is that this finish can flake off into the coolant fluid and degrade the image performance of the lens system. Another disadvantage in the current system is the need to perform a secondary machining process to the sealing areas of the coupler due to the rough surface finish of a die cast part. Still another disadvantage is the fact that the coupler does not contain any way to rotationally orient the “C” lens element. This is a common practice done manually during the assembly process.